This is a known bug
It can be resolved by looking away from the cockpit glass panels.
Adjust your views so the cockpit glass panels are no longer on your screen. Ie look at the roof of the cockpit or the outside. It takes a while to recover it’s not instant. At least 30 sec to 1 min if not more.
Going external views won’t help I think. Stay in cockpit and look at the roof or the outside.
Yea… I’ve had the men in black spawn once. Maybe that’s the Flight Sim check ride pilots… 
Hey… I just tried your suggestion but it didn’t work. I actually left the screen toward the left away from the cockpit the entire flight (after reaching cruise) just to test it out but the same thing happened. After about 3 hours frames dropped to 5 FPS with the 787.
That’s unfortunate.
There is no need to look away for the rest of the flight. Only after the FPS drop.
I had this happen in a GA plane and it worked. 787 is known for having Ridiculously low in-cockpit FPS. Maybe you need to wait for a bit longer? If that still doesn’t work, then I’m out of ideas.
I had the same issue now in my flight after about 1 hour suddenly the FPS dropped from 45-52 to about 10-15. I dissabled the VFR map from the top menu and the FPS went straight back to 45-52.
Just did 2 ultra long haul flights with 1.11.6.0/ World Update 2, this issue doesn’t seem to exist anymore! 
I think they fixed a memory issue associated with the auto-gen airplanes… The simulator would never forget them once generated so the system memory would fill up as time went on.
I’m not computer expert…well…I was one before I retired last year. LOL
This may be a memory usage issue. By the time I reach 6-7 hours in the air in Citation or one of the airliners I’m down to a slide show at 8 -10 FPS. Task manager shows performance as expected except FS2020 is now using over 8 GB RAM. I am not using any mods just a couple of small scenery addons. I know they don’t affect this, or it wouldn’t take 7 hours to show up. I was no where near the scenery when flying, but I tried it with no scenery addon loaded. Same issue. I can reproduce this issue reliably. I just need 6 - 7 hours. LOL
Good hunting everyone. Let’s step on this bug! (Memory leak?)
With 16GB of RAM the sim normally runs at around 10-12GB used (only uses more at heavy photogrammetry areas). So I’m not surprised at all that 8GB is filled up really fast.
You can take a screenshot anytime you want now:
[TIP] Add a copilot to your aircraft (and passengers too!)
I wish I knew because after the simulator dying on me in VR (CTD) right when I’m in the middle of my final approach after long flights, 3 times already, I really don’t want to make any serious simming with this anymore.
I increased the size of the page file and I am still getting the fps down to 10 or less after a 7 hour flight across the Atlantic ocean (Not to many objects to render over the ocean.) I have an Alienware Aurora R9 with 32 Gigs RAM. Geforce 2080 super video card with 8gigs vram. I really hope hardware is not the issue.
I have not tested this yet but will when I have time for another long flight. I will report back here. I read a post on another forum which suggested that the sim is generating cars and boats and other planes constantly and that once they’re generated they are not being deleted and they build up over time taking all your resources to maintain. I am going to turn down all the boats and cars etc. (I have never changed the default settings.) I will report if that helps or perhaps another pilot here could test it also and report back here sooner. Good luck gentlemen!
Let me add that short flights are not a problem, 60 frames consistently or more and one other post I found off this site mentioned that perhaps they never planned for pilots to make trans-ocean or other very long flights. I’m pretty sure that isn’t right.
I lowered all the cars, boats and ships and ferries settings to very low settings and I was able to run a long trans-atlantic flight to test. The frame drop was better only dropping to 20 - 24 FPS, Still a very far drop from 60+. I don’t know if the cars and boats is the actual issue or if turning them down only helped slow down the issue from dropping me into single digits.
I have an alienware aroura 9 with an nvidia 2080 super. I can’t imagine hardware is the issue. If so I feel for anyone with lower specs. There is another thread on this forum where you can vote up this issue and hopefully Microasobo will fix it.
Check the memory usage of FS2020 in the resource monitor (task manager performance tab, bottom left).
I find that the committed amount of memory sometimes gets very high after long time flying, I’ve seen it go over 40GB, which results in a huge page file and lots of page faults. It’s not actively using that much memory, but it’s severely fragmented forcing windows to continually swap pages in and out (hard faults / sec) causing slow down.
After restarting in exactly the same place, memory is down to 18GB committed again. It usually happens over areas with lots of trees.
Thank you SvenZ. I will try that ASAP and report back. I get this when I take off on the west coast of Europe, like Heath Row or some airport right on the coast. I have AP fly the plane while I rest or do other things then come back in time to land. 99.99% of this test flight is over open ocean, no trees, cars maybe a few boats and planes but I never see any.
When you say “restarting” I believe you mean saving the flight and then restarting FS2020? If that is correct that would be a good work around but not really a fix. The fix for a memory leak has to come from the developer. Search this forum for similar posts, there is one I am having a bit of a hard time finding again where you could vote this issue up. That may help if enough people report this as an issue. Thanks again.
Maybe not related to this but I have had the “exact” same expeirence with long flights.
On my end, not saying this is universal, I am experiencing a memory leak. I have noticed that some textures do not get unloaded and stay in memory untill it gets full. With 32GB RAM, in this sim, it is not enough. I start the sim on some airports at 26GB, especially at custom airports.
Not enough left to play with…
I can reproduce the issue consistently and reliably. All I have to do is plan a long flight over the barren ocean, and then just wait a few hours. I have fiberoptic internet with 1000 up and 1000 down so I can and have completely uninstalled and reinstalled. (Twice. It’s crazy to expect a different result doing the same thing over and over, but I did it. LOL) I have checked the files through steam. I have enlarged my page file. I turned down all the objects like cars and boats to barely on. Nothing helps. After a few hours frames drop. After a couple more hours it devolves into a power point slide show 9 - 11 FPS which is as low as I have seen it get, but it is of course challenging to land a widebody heavy at this frame rate. LOL
I really didn’t need to test the save and restart suggested by SvenZ. I realized this is the work around I have been using. All longs flights now end with the escape key. Hope this gets fixed. Saving your flight and restarting FS then picking up where you left off is the best work around I have found until when and if a fix is found.
If you google something like “MS flight simulator fps drop after long flight” you will see several threads including one that I just found that suggested it was the glass cockpit refresh rate or popping out a window like the VFR map. Evidently you can change the glass cockpit refresh rate in settings. I think these issues are yet another issue as they say it happens in a much shorter flight than we are discussing here. I take off on the coast of Europe, and let A320 fly over the Atlantic, slowly 250 Kts, on AP while I sleep, wake up it’s not yet approaching the US coast but down to 11 FPS and dropping, over the barren ocean just a few clouds. I’ll try anything but at this point I believe we have to live with it until someone like one of the Asobo devs steps in with a fix. If I find a good fix I will return here and post it.
Good luck gentlemen and thanks again for you help.
Anyone remember “Flash” from back when we ran FS on DOS and it came on 4 floppy disks? That was me. 
Had the same issue after bit more then 4hrs in the NEO today.
Disabled then the VFR map in the toolbar and worked instant fine again.
I happened to me again today. No clue why, just flying over pretty much empty desert as you can see in the background.
After restarting the game, continuing from the same airport, 17 GB committed instead of 36GB and 10 GB working set, no hard faults
By disable the VFR map do you mean close it or is there a setting somewhere to disable it? I don’t open it. I use the garmin screens in the cockpit. I take off in a Citation or NEO320, turn on the AP and check back a little later, if I have not flown into a mountain the flight is continuing only FPS has dropped from 60 to 9 or 10. I can reproduce this with a flight over the open ocean or deserts below Egypt where I don’t see anything to be rendered, maybe a stray boat in the ocean but I have all cars and ships and planes turned down trying to do long flights. If the VFR map is the problem they should be able to patch it, I hope. Thanks.
For now I am sticking to shorter flights and hope this gets addressed. Thanks All.
just disable it via the toolbar at the top of the screen via the cog icon.
don’t disable any other way as it can STILL do the FPS drop, in which case you then need to enable the VFR map again and open it and even undock it to its own window before closing it again and re-disabling it via the cog once more.
i.e. having the VFR map disabled via the cog so you can re-enable when the FPS problem strikes seams to cause a purge of the problem most of the time.
